Ok, question from the new guy..., or old lurker. I'm running a 350 crate motor in my Toyota 4runner, and I recently had a problem. I was running in sand dunes in Michigan and lost 2 cylinders. Story short, crushed 2 valve springs on two different exhaust valves. My question is... why would this happen? I'm running an RV cam, which is a little higher lift than normal.

I thought it might be due to over rev, but now I'm not so sure, seems like the sand dunes was the straw that broke the camels back. The motor has about 50K of hard wheeling on it.

The supposed machinist at the local parts store said it was probably due to the higher lift cam, and the exhaust roto cap
(the cap that rotates the exhaust valve a little each time it opens) supposedly its common to remove these when running a higher lift cam???:confused: he said the roto cap was shortening the stroke of the spring
CAN anybody help??? I changed springs to higher tensile type, but now I have hard start + idle problems. I'm wondering if I should go back to regular springs + no roto cap:confused:

#1 contact the cam mfg.

#2, measure, at max lift, the spring compression then get the specs on your springs and make sure they can compress that much.

THE VALVE SPRINGS REALLY HAVE NOTHING TO DO WITH START UP OR IDLE.....UNLESS THEY ARE SOME CRAZY ASS HIGH PRESSURE RACE SPRINGS OR SOMETHING.

MAYBE WHEN YOU BUSTED THE SPRINGS YOU WACKED A VALVE ON THE PISTON BENDING IT???

HOW DID YA FIGURE OUT YOU HAD BROKEN VALVE SPRINGS ANYWAYS?

WITH A FLAT TAPPET CAM YOU CAN RUN A FAIRLY GOOD SPRING WITHOUT ANY PROBS,THE MORE SEAT PRESSURE YOU GO WITH THE CLOSER YOU GET TO HAVING TO RUN A ROLLER, BUT WITH ONLY AN RV CAM STOCK SPRING SHOULD WORK FINE UNLESS YOUR IN THE HIGH RPMS A LOT...THEN IT WILL FLOAT THE VALVES.

I noticed I had a solid miss fire at all RPMs, checked the compression and basically had ~25 psi, so I pulled the valve cover, and noticed the spring was broken in about 3 places. Wasn't till I tore it down a little when I found the 2nd broken one.
I admit, I have floated the valves a few times, usually in low lock 1 with foot to the firewall.

I think I'm gonna go back to the stocker springs & put in the roto caps & lay off the go pedal a little. Lasted 50K miles like this, should last another 50 more.

I'm not sure what these stronger springs are, but I've never had the starter hesitate when starting, and it seems as if it takes a crapload more torque to roll it over.

Originally posted by pfreer3
I admit, I have floated the valves a few times, usually in low lock 1 with foot to the firewall.



Gee, this sounds familiar. Pull the heads, I'll bet you have eyebrows on your pistons. BTDT and have the broken parts (valves, valve springs, ring/pinion with missing teeth) to prove it.

SBCs will take a lot of abuse, but it only takes over-revving a few times for the carnage to begin.

If you got 50K out of it with this kind of usage, I'd say you got your money's worth.

Peace,
Paul

Chevy crate motor=made in mexico!

Originally posted by PTSchram


Gee, this sounds familiar. Pull the heads, I'll bet you have eyebrows on your pistons. BTDT and have the broken parts (valves, valve springs, ring/pinion with missing teeth) to prove it.


When I first read your post, I was thinking "hmm, sand dunes. Wide open throttle, little traction, jumps, valves floating."

I'm with Paul on this one.
Every motor I have ever torn up was due to the skinny pedal.

Looks like it got you too.
One way to combat this in the future is with a rev limiter or by under-carbureting the motor. Not enough fuel, can't peak the revs, but this also hurts throttle response.

I did pull the heads, and had the valves re-ground and re assembled with a heavier spring. I didn't see any other damage inside the motor. No "eyebrows" on the pistons, or damage to valves. I was pretty suprised, same as you guys. I expected hole in piston, when I saw the broken spring. Actually valves didn't need regrind on the seat only a little on the stem end, due to a couple didn't pull out of the guides so smooth. Probably due to rocker wear. Besides broken spring, I didn't notice hardly any damage, which is why I decided to put it back together VS. new crate motor.

Yeah, its a Hencho en Mexico, but I'm pretty impressed with it so far. After I get this bug worked out, I've got a guy building a tuned port intake + ECM for me. After that, no more black smoke out the tailpipe on hills!

Usually, if you don't lose the head of the valve, you won't find a perforated piston.

You got lucky this time, very, very, very lucky. Might consider a rev limiter, much cheaper than roller cam and associated components to be able to handle the higher RPMs. I'm not sure I'd go with the smaller carb for fear of going too lean and Burning a hole in a piston, versus puching one. Kinda like the idfference between a torch and an ironworker:flipoff2: